This invention relates to an image pickup system for use in combination with a craft, such as a spacecraft, flying over an object zone which is typically on the ground surface of the earth. Such an image pickup system is particularly useful in a remote sensing system for the earth.
An image pickup system of the type described is used to remotely sense an object zone on board a craft flying over the object zone along a flying direction at a predetermined flight altitude. In a remote sensing system, it is often necessary to pick up a stereo image, such as a stereo topographic image, from the object zone by the use of the image pickup system. In order to provide the stereo image, the object zone should be picked up, along the flying direction at two positions spaced apart from each other, so as to form two optical images of the object zone.
A conventional image pickup system is disclosed in U.S. application Ser. No. 410,104 filed Sept. 20, 1989, by Naoshi Suzuki and for assignment to the instant assignee. In the image pickup system, an optical system is used on the craft to form, on a focusing area of the optical system, optical images of forward and backward zones lying transversely of the flying direction in the object zone. The forward and the backward zones are positioned at a predetermined distance along the flying direction. Forward and backward optical images are picked up from the forward and the backward zones. The forward and the backward optical images are transduced into forward and backward electric signals by using forward and backward photoelectric transducers, respectively, placed on the focusing area with a gap left therebetween. The forward and the backward electric signals are transmitted from a transmitter of the craft to a ground station at a predetermined transmission rate.
Transmitted from the craft, the forward and the backward electric signals are produced so that the forward and the backward optical images are reproduced in the ground station to provide the stereo image. In practice, the forward electric signal is delayed by a predetermined time duration into a delayed signal in the ground station. The predetermined time duration is such that the delayed electric signal appears concurrent with the backward electric signal. In other words, the delayed signal is produced after the craft flies the predetermined distance.
A recent requirement is to provide the stereo topographic or a like image at a high resolution so as to make up a precise stereo topography or the like. This requirement gives rise to an increase of the forward and the backward electric signals in number. This means that it is necessary to carry out data compression of the forward and the backward electric signals. In this event, the craft must carry the memory having a large capacity. It is undesirable that the memory has a large capacity because the craft is restricted in size, power consumption, and weight.